The present invention relates to a cleaning system that uses ice blasting and particularly to a system that uses coated ice particles as the cleaning agent.
Sand or grit blasting--propelling small granules of abrasives, such as sand or glass beads, towards surfaces such as walls, floors, and ceilings--has been widely used to clean surfaces that are dirty or have an unwanted coating (such as paint or graffiti). Grit blasting has several problems. For example, grit blasting is extremely abrasive which is damaging to the surface being cleaned. Also, the abrasives are expensive to obtain and become contaminated with the removed material after one use. Further, once the abrasives are contaminated they must be collected, a time consuming and often difficult proposition, and properly disposed since contaminated abrasives are usually not reusable. Since disposal costs are based on the weight of the material to be disposed, disposing of the abrasives along with the contaminants is extremely expensive.
Ice blasting, a process that uses ice or frozen material instead of traditional abrasives, solves some of the problems of grit blasting. For example, ice is generally not abrasive. Another example is that, if water is the frozen material, it is relatively inexpensive to obtain and is generally only needed in small quantities. Also, depending on where the ice blasting is being done and the type of coating that is being removed, the contaminated ice particles often can be allowed to melt and evaporate and thus little or no collection would be necessary. Still further, depending on the removed material, disposal may be done after the water has evaporated which leaves only a small amount of removed material for disposal.
Ice blasting has several other advantages. For example, it can remove soft or hard coatings such as grease, tar, paint, and even radioactive contaminants without damaging the underlying substrate. It is also dustless.
Stratford et al. U.S. Pat. No. 5,203,794, Fong U.S. Pat. No. 4,038,786, Moore U.S. Pat. No. 4,617,064, and Fong et al. U.S. Pat. No. 4,389,820 disclose blasting apparatus that uses sublimable particles such as CO.sub.2 as the cleaning agent. Although these devices are generally preferable to grit blasters, they still present several problems. For example, CO.sub.2 generally comes in particles or in a dry ice block and is therefore expensive. Also, CO.sub.2 is more difficult to obtain than water.
Visaisouk et al. U.S. Pat. No. 5,367,838, Ichinoseki et al. U.S. Pat. No. 4,655,847, Westergaard U.S. Pat. No. 4,703,590, and Kelsall U.S. Pat. No. 4,965,968 are directed to ice blast cleaning systems that can use ice formed from water as the cleaning agent. The ice blasting systems disclosed in these patents are troublesome, complicated, limited in use, and very expensive.
More specifically, the known ice blasting systems are troublesome to use because they have configurations that have ice flow that is very unstable and requires frequent adjustments. Further, these systems suffer from recurrent ice build-ups or ice plug-ups that cause expensive machine operation delays. These ice build-ups or plug-ups often occur when the temperature of a system raises above freezing and then goes below freezing again. Accordingly, known systems do not function properly in environments above freezing.
To prevent ice build-ups and ice plug-ups, known systems use complicated designs because they must stay below freezing in order to function. Accordingly, all or part of each of these systems has to be cooled down to below freezing which uses significant energy and adds complicated and costly cooling and control devices.